This invention relates to vehicle headlamps and, in particular, to rectangular vehicular headlamps adapted to produce one or more light beams, at least one of which is a depressed beam suitable for use when passing vehicles traveling in the opposite direction.
In the automotive industry, the size, shape, and placement of headlamps as well as the optical performance of headlamps are subject to regulation by an agency of the Federal Government. A recent change in these regulations has enabled the use of headlamps having a rectangular shape when viewed from the front.
The rectangular shape of the lens is enabled by cutting the paraboloidal reflector with planes (herein referred to as "sidewalls") to produce the desired shape at the open end of the paraboloid. When glass having the prescribed shape is aluminized (given a reflective coating, usually on the inner surface of the paraboloid), the sidewalls are also made reflective.
A finished lamp, having the reflector thus described, produces considerable glare in use, i.e., undesirable high levels of light. On the "low beam" setting, extraneous light has been found above the correct high intensity area of the beam pattern. Much of this light comes from the lower sidewall of the lamp. Light reflected from the upper sidewall, when further reflected by bumpers or other reflecting surfaces around the headlamp, adds to the glare, as does light from the left and right sidewalls. This glare makes it difficult to meet the government regulations noted above and makes the lamp inferior in adverse weather conditions where backscatter impedes visibility, e.g., rain, fog, and snow.
The problem has been recognized in the industry, and the solution to date has been to burn away some of the coating from the sidewalls of the lamp. Unfortunately, when the coating is removed from the sidewalls, it is also removed, to a lesser extent, from the paraboloidal surface. This reduces the effectiveness of the reflector and, hence, the maximum candle power of the lamp. In addition, the burning process is not uniform from lamp to lamp and is detrimental to lamp appearance.
In lower beam headlamps, round or rectangular, a filament shield is used over the lower beam filament to prevent light from the filament from going directly to the lens. In round lamps, control of the beam is thus assured by the reflector and the lens prescription. So far as is known, no one has proposed using a filament shield to prevent light from reaching portions of the reflector of a headlamp. For example, see U.S. Pat. Nos. 2,277,563; 2,366,292; 2,858,467; 2,880,347; 2,987,643; and 3,136,914, in which the filament shield does not cut off the filament light going to the reflector. In U.S. Pat. Nos. 2,795,722 and 3,908,144, it may appear that such is the case. However, what is actually provided are two sets of optics in a single structure to obtain a two-color light output, usually red and white.